Process systems are being operated longer and longer (e.g., five to eight years) between shutdowns that are short and shorter (e.g., thirty to forty-five days). Moreover, the control valves of many process systems are being operated within five to ten percent of a particular position over most of their period of service. These circumstances result in control valves being operated longer and closer to the end of their operational life.
Traditional diagnostic techniques for control valves have involved taking a process system offline and removing the control valve from the process system. The control valve is then sent to a laboratory where characteristic signatures are made and compared to baselines. Performance characteristics such as dead band, hysteresis, and full-stroke operation may be characterized. Unfortunately, this type of diagnostic technique is time consuming and costly to perform (e.g., sometimes requiring extensive effort to remove insulation, heat traces, and steam traces from the control valve and a crane to remove the control valve from the process system), leading to large process system downtime and expense.